Much attention has been given to the fact that cellular activity can be controlled by the minute patterns and three-dimensional structures of material surfaces, and such techniques have been the subject of numerous recent reports in the field of tissue engineering. The development of technologies for forming minute structures with the optimal size, surface structure and spatial creation for cells has come to play an pivotal role in achieving freer design of biological tissues.
For example, cartilage tissue contains no blood vessels, nerves or lymphatic ducts and therefore has poor regenerative capacity. Consequently, damaged sites are not regenerated and they lose their original function. Known clinical conditions involving loss of articular cartilage include diseases such as osteoarthritis and rheumatoid arthritis, and injury-induced articular cartilage damage. Artificial cartilage replacement surgery is performed for repair of such poorly regenerable cartilage, but because artificial cartilage includes metals and high molecular polymers it is susceptible to abrasion, loosening, infection and the like. Another strategy employed is transplantation of chondrocytes, but once damaged cartilage can only be regenerated as fibrocartilage, which is biochemically and dynamically inferior to the original hyaline cartilage. Therefore, a recent tissue engineering technique that is being actively researched is chondrocyte transplantation utilizing a scaffold with a three-dimensional structure in order to maintain the properties of cells.
One such technique is disclosed in Japanese Unexamined Patent Publication No. 2001-293081, as a cartilage transplant material having chondrocytes embedded in a collagen gel. However, if collagen is not handled at low temperature it gels and can no longer mix with cells, while its gel strength is also weak.
U.S. Pat. No. 6,197,061 discloses a method of growing chondrocytes in an alginate gel. However, the alginate gel is decomposed after use for cell growth and therefore in practice performs no function as a scaffold for injection of chondrocytes into affected areas.
Also, Japanese Unexamined Patent Publication No. 2001-157574 discloses the cell culturing substrate of a honeycomb structured film comprising a biodegradable polymer and an amphipathic polymer, but this publication nowhere refers to a cell culturing substrate and chondrocytes in a biodegradable film with a honeycomb structure comprising a phospholipid.
Furthermore, Japanese Unexamined Patent Publication No. 2002-335949 describes a method of forming a three-dimensional aggregate of hepatic tissue or myocardial tissue using the cell culturing substrate of a honeycomb structured film comprising a biodegradable polymer and an amphipathic polymer, but this method involves forming a multilayer structure by growing cells on both sides of the cell culturing substrate, whereas the cells themselves do not grow in a three-dimensional structure.